There are a number of orthodontic techniques in use, the most common being the edgewise and the Begg techniques. Within the ambit of the edgewise technique, the most popular form is referred to as the straight-wire technique, although all forms of edgewise technique generally use edgewise brackets having horizontally extending archwire slots, the openings of which face horizontally. The bracket configuration for the Begg technique utilizes a vertically extending archwire slot which permits materially greater free tipping of teeth during treatment than heretofore known edgewise brackets. Free tipping action with edgewise brackets is very limited and only possible when a wire smaller than the archwire slot is employed, so that there is a sloppy or loose fit between the archwire and the slot.
The need for moving teeth mesial-distally is usually caused by spaces created by small or missing teeth. It is customary in the Begg technique to close these spaces or move teeth by first tipping the clinical crowns toward the open area and then uprighting the root so that the final uprighting or tip angle of the tooth is at a predetermined inclination. For closing such open sites when using the edgewise technique, it is customary to bodily move the teeth. It is well known that the forces needed, discomfort, and time required for closing spaces by tipping and uprighting movements is much less than that required for bodily moving the teeth.
Where teeth are initially tipped and standard edgewise brackets are mounted on the teeth to provide treatment through the edgewise technique, it is difficult, if not impossible, to engage a relatively large diameter or stiff archwire into the respective archwire slots. The same problem exists if teeth with edgewise brackets become tipped during the course of treatment. And yet, such larger diameter, stiffer archwires are often necessary to control the vertical and horizontal positions of the teeth in the jaws. Therefore, weaker and more flexible archwires must be utilized which can cause the anterior teeth to elongate. The most common method of preventing elongation includes application of heavy extraoral forces to the upper archwire.
If resilient archwires are deflected to fully engage edgewise slots where teeth are tipped, the occlusal plane or level of the biting edges of the teeth can be adversely affected by the forces applied through these archwires. Usually, the anterior teeth are elevated out of their sockets, resulting in an unhealthy deep anterior overbite condition. This is one of the reasons tipping of teeth in the edgewise technique is avoided. Moreover, the very design of the well known edgewise bracket prevents teeth from becoming tipped during treatment. It will be understood that the "occlusal plane" as used herein is a plane generally containing the contact points between the upper and lower teeth, and it generally lies ninety degrees to the vertical lines used for references when determining and describing the amount of tip desired for each tooth.
In Begg brackets, sometimes referred to as ribbon arch or light-wire brackets, it is usually possible to engage larger stiffer archwires in the archwire slots because the opening of the slots face vertically, thereby permitting ease of archwire engagement in brackets mounted on tipped teeth.
It has been suggested that the edgewise slot be shortened mesiodistally or altered to define opposing one point contacts to increase the degree of tipping. However, the former still restricts tipping, and the latter (altered) bracket can permit free tipping but has no ability to control or create the final, desired degree of uprighting.
While Begg brackets that permit but limit tipping and/or uprighting are known, edgewise brackets with similar functions are not known.
It has also been known to use combination brackets having both labially or horizontally facing horizontal archwire slots and gingivally facing vertical archwire slots where the vertical slots would be used during early stages of orthodontic treatment to allow the crowns of the teeth to tip toward their final positions. Then in the final stage an archwire can be deflectively received by the horizontal slots. However, while this will tend to upright the teeth, it will also tend to deepen the anterior bite condition and therefore headgear for producing extraoral forces may be required to counteract such adverse conditions. Headgear comprises using the patient's head or neck as a point of anchorage for delivering relatively heavy forces to the teeth.
Where combination brackets are used, it has also been suggested that two archwires be used, one in the horizontal slots and one in the vertical slots. A lighter more resilient archwire is deflected to seat in the angulated horizontal slots, while a heavier stiffer archwire is engaged without deflection into the vertical slots. The heavy wire helps stabilize the reciprocal forces delivered to the teeth from the lighter deflected archwire as it returns to its passive straight arch form. The use of two archwires is cumbersome and creates undesirable food traps.
In the edgewise procedure teeth are moved bodily in their upright positions toward one another to close spaces. Such movement requires two to three times as much force and time as when moving teeth in the Begg technique by a combination of tipping and uprighting forces. Normally, the crown tipping is followed by root uprighting. Moreover, the bodily movement method in the edgewise technique most often requires the application of extraoral force supplied by headgear. Clinical experience indicates that the use of such extraoral force has caused hundreds of soft tissue injuries including many cases of partial and even total blindness as a result of accidents occurring while wearing headgear.